Earth rotation from radio interferometric tracking of GPS satellites

Abstract

Radio-interferometric tracking of the Global Positioning System (GPS) satellites offers a new technique for regular monitoring of variations in the earth's rotation. The observations are sensitive to pole position and length-of-day, at a level of precision which may make this technique competitive with satellite and lunar laser ranging and very long baseline interferometry (VLBI). The present limitations are the number of satellites and tracking stations available and inadequate modeling of non-gravitational forces on the satellites. The potential advantages are rapid turn-around and minimal incremental cost. We have performed a preliminary analysis using six days of observations from a four-station network. Comparison of earth rotation values from our GPS analysis with values obtained by VLBI and laser ranging reveals differences after five days of 0.9 ms in UT1, 0.04″ in x and 0.07″ in y. These differences reflect errors in the GPS determinations due primarily to inadequate modeling of non-gravitational forces.